Properties of ionic liquids containing silver(I) or protic alkylethylenediamine cations with a bis(trifluoromethanesulfonyl)amide anion

Ionic liquids of an N-alkylethylenediamine-silver(I) complex cation (alkyl = hexyl, 2-ethylhexyl, and octyl) or a protic N-alkylethylenediaminium cation (alkyl = butyl, hexyl, 2-ethylhexyl, octyl, decyl, and dodecyl) with a bis(trifluoromethanesulfonyl)amide counter anion (Ag-ILs and PILs, respectively) were prepared and their physicochemical properties were investigated. The trend of solidification decreased in the order octyl ≫ hexyl > 2-ethylhexyl for the Ag-ILs, and butyl > dodecyl > decyl > octyl > hexyl ≫ 2-ethylhexyl for the PILs. The diffusion coefficients of the cations indicated stronger intermolecular interactions in PILs than in the Ag-ILs because of hydrogen-bonding networks, and it has been revealed that the intermolecular interactions increase in the order, hexyl < octyl < 2-ethylhexyl for the Ag-ILs, and hexyl ≈ 2-ethylhexyl < butyl ≈ octyl < decyl ≈ dodecyl for the PILs. The ionicity of the PILs was nearly independent (0.38–0.43) of the lengths of the alkyl chain. The octyl Ag-IL provided uniform silver(0) nanoparticles upon reaction with aqueous NaBH4 solution, whereas the 2-ethylhexyl and hexyl complexes did not form silver(0) sols. This difference can be attributed to the ordering of the nanostructures in the Ag-ILs.

Formation of silver(0) nanoparticles by the reaction with aqueous NaBH4 solution depends on a slight difference in the alkyl chains of the silver(I) ionic liquids.Figure optionsDownload high-quality image (68 K)Download as PowerPoint slideResearch highlights
► Novel ionic liquids having ethylenediamine head group were prepared.
► Ethyl side-chain is effective on the physical properties of Ag-ILs and PILs.
► Both the hydrogen-bondings and alkyl chains govern the unique properties of PILs.
► Formation of silver nanoparticles depends on the ordering of nanostructures of Ag-ILs.